The International Astronomical Union officially recognizes five dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris.
The category was established in 2006, when the IAU defined a dwarf planet as an object that orbits the Sun, is nearly round because of its own gravity, has not cleared its orbital neighbourhood, and is not a moon. Pluto was reclassified under this definition, while Ceres was promoted from asteroid to dwarf planet.
The five recognized objects occupy different regions. Ceres lies in the asteroid belt between Mars and Jupiter; Pluto, Haumea, Makemake, and Eris orbit beyond Neptune. Haumea was the last of the five to receive official recognition, in 2008.
The number five can be confusing because astronomers have identified several additional bodies that probably meet the physical definition, including Gonggong, Quaoar, Orcus, and Sedna. However, those objects are not part of the IAU’s officially recognized set, so a quiz asking specifically about IAU recognition has a canonical answer of five.